The present invention concerns an access network for mobile terminals of the type which consists of a switch connected on the one hand to at least one other external network and on the other hand to a local access network itself connected to a plurality of radio base stations, each base station being designed to enter into communication with mobile terminals.
The present invention is situated in the context of access networks for mobiles based on ATM (Asynchronous Transfer Mode) technology. More precisely, it concerns access networks for mobiles which are based on end-to-end ATM technology, both in the control plane and in the user plane. Consequently the mobile terminals envisaged in the present invention support applications which justify the use of this ATM technology designed for the transfer of data at high speeds. Amongst these applications there can be cited, by way of example: video telephony, high-speed data transmissions, the consultation of Internet servers, etc.
The patent document U.S. Pat. No. 5,787,077 describes a network whose ATM technology is used end to end.
In the known networks for access to mobiles, ATM technology is envisaged only as far as the access to the radio base station, also referred to as the base station. In these known networks, the mobile terminals cannot support the stacks of the protocols which are specific to this ATM technology. Also, the targeted field of application is generally that of cellular radiocommunication networks.
In the document U.S. Pat. No. 5,787,077, the fact that ATM technology is used end to end, both in the control plane and in the user plane, means on the one hand that the items of information transmitted over the radio medium between the mobile terminals and the local network are ATM cells, and on the other hand that the signalling messages for establishing calls which are transmitted or received by the mobiles and the switch are in accordance with the standards recommended by the ITU.
In general terms, in ATM technology, each virtual connection is identified by a virtual path identifier and a virtual circuit identifier. One of the problems resolved by the technique described in the document U.S. Pat. No. 5,787,077 mentioned above is that of the adaptation of the virtual path identifiers and the virtual circuit identifiers to the radio environment between the base stations and the mobile terminals.
A recurrent problem with access networks for mobile terminals is that of mobility. When a terminal moves whilst it is within the coverage of an access network, it may be attached to a first base station, then to a second base station at the same time as the first, and then to the second one alone. These changes in attachment of a terminal give rise to modifications to the virtual connections between the said terminal and the said base stations concerned through which the user data pass.
These modifications to the virtual connections should therefore give rise to corresponding modifications to the identifiers.
In the document U.S. Pat. No. 5,787,077, when a mobile terminal enters into the coverage of an access network, the latter assigns to it a virtual connection identifier. The virtual path identifier in the access network is determined in relation to the virtual connection identifier. Virtual channels are used so that a terminal can use more than one logical connection.
When the mobile terminal is in the process of changing base station, a new virtual connection identifier is defined as well as a new virtual path identifier in the network.
With regard to the signalling plane, several designs are provided for in the document U.S. Pat. No. 5,787,077, amongst which it can be cited that a predetermined pair of virtual path and circuit identifiers are defined on the wireless interface so that each terminal in the system uses the same pair.